mxs_ocotp: prevent error path from returning success

mxs_ocotp: prevent error path from returning success

The code may goto 'fail' upon error with 'ret' variable set to an error
code, but this variable was being overwritten by a final preparation
function to restore the HCLK, so success was (in general) returned even
after an error was hit previously.

With this change, the function may now return success even if the final
preparation function fails, but it's probably enough to print a message
because (if successful) the real programming of the fuses has already
completed.

Signed-off-by: Hector Palacios <hector.palacios@digi.com>